Oberheim Two Voice

Oberheim's first synthesizer was a single-voice mini-module called a SEM (Synthesizer Expander Module). However, in
1975, Oberheim created their first compact, programmable and polyphonic
synthesizer by coupling two SEM modules to a 37-note keyboard and a
simple analog sequencer. This was what became the Two Voice. Oberheim
achieved a polyphonic sound not yet seen in ARP and Moog gear at the
time by hard-wiring the two monophonic SEMs into the compact keyboard
design.

In 1976 Oberheim came out with another module, the Polyphonic
Synthesizer Programmer (see SEM). This could
memorize the control voltages of many parameters for up to eight SEM
modules. When these were added to the Two Voice, Oberheim finally had
one of the earliest programmable and polyphonic instruments! Released
alongside the Two Voice also came the Four
Voice which had four SEMs installed, and a larger 49-note keyboard.
And later, in 1977, a second tier was added above the four SEMs on the
Four Voice to add yet another four SEMS, making the Eight Voice.

Two voices was great in 1975, and eight voices was pretty monstrous in
the later seventies. But, a major drawback to these first Oberheim
synths was that polyphony was achieved by having multiple modules. This
meant that each voice had to be independently programmed. This also
means that each voice has its own filter, making real-time filter sweeps
of all your voices more than a handful! Fortunately the sequencer comes
in handy for controlling each voice/module independently.

Despite its innovative features, the Two Voice was soon blown out of the
water by the popular monophonic and truly polyphonic synths like the OSCar, ARP Odyssey and SH-101. The Two Voice has been used by
Vince Clarke and Vangelis.

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